It is known to produce two stoke engines of the rotary piston type with a cylinder block, housing a plurality of cylinders, rotatably mounted within the engine housing.
Once such rotary two stoke engine is disclosed in WO 99/18322 (Gahan). This engine includes an engine housing supporting two main bearings within which a crankshaft rotates. A crankcase is configured to rotate over the crankshaft, the crankcase being rigidly attached to the cylinder block which houses opposed cylinders. Each cylinder, in turn, houses a corresponding piston which is slidable within the cylinder. It may be appreciated that, in this configuration, the crankcase, cylinder block, cylinders and plurality of pistons housed therein are able to rotate about the two main bearings relative to the engine housing.
The crankcase is coupled to the crankshaft via a series of gears configured such that rotation of the crankshaft causes likewise rotation of the crankcase and cylinder block, about the two main bearings. The pistons are connected by connecting rods and associated crankpins to the crankshaft such that movement of the pistons causes the connecting rods and associated crankpins to move thereby rotatably actuating the crankshaft. As aforementioned, this rotation of the crankshaft, in turn, actuates the gears which couple the crankshaft and crankcase, so that the cylinder block and pistons therein rotate about the main bearings in response to movement of the pistons.
The series of gears that couple the crankshaft to the crankcase are provided in the form of elliptical gears which provide a gear ration of 2:1 between the crankshaft and the crank case. The elliptical gears include a crankshaft gear located on the crankshaft, a crankcase gear positioned on the crank case and two “piggy back” idler gears configured to be placed between the crankshaft gear aid the crankcase gear. The idler gears are configured place the crankcase gear in positive rotary engagement with the crankshaft permitting 360 degree rotation of the crankshaft to result in 180 degree rotation of the cylinder block.
It may be appreciated that in this configuration, the elliptical gears reside in a relatively confined space defined by the inner walls of the crankcase and the outer walls of the crankshaft. As such, there are limitations on the size of gearing, for example, the idler gears are required to be small. Moreover, although the configuration of the elliptical gears may assist to reduce loading on the crankshaft, the loading now is taken by the elliptical gears, particularly the idler gears, which are now subject to high loading and high rotational speeds.
The opposed cylinders housed within cylinder block are provided in the form of two pairs of opposed cylinders. The pairs of cylinders, housed within the cylinder block, are spaced apart relative to the axis of rotation of the crankshaft with their respective connecting rods and associated crankpins coupled to the crankshaft at laterally spaced positions.
Each piston within the cylinder has an elongated stem between an upper annular flange spaced apart from a lower annular flange, so as to present an I-shape cross section. The connecting rod extending between the lower annular flange and the crankpins couple the connecting rod to the crankshaft.
The cylinders are configured to provide a housing sized such that the piston is able to move from a top dead centre position (TDC), where the upper annular flange adjacent an outer face of the cylinder positioned distal to the crankshaft, to a bottom dead centre (BDC) position where the lower annular flange is positioned adjacent an inner face of the cylinder proximal the crankcase. As such, in the TDC position an induction chamber is defined between the lower annular flange and the inner face of the cylinder while in the BDC position and a power chamber is defined between the upper annular flange and the outer face of the cylinder. Additionally, an ancillary chamber open to the atmosphere is provided between the upper annular flange and the lower annular flange.
Accordingly, it may be appreciated the induction chamber, power chamber and ancillary chambers are coaxial and are radially symmetric about the stem of the respective piston.
During operation, air and fuel is communicated via a port into the power chamber and the piston then moves upwardly toward TDC. As the piston moves the crankshaft is actuated via the connecting rod, which in turn rotates the crankcase and hence the cylinder block. As the cylinder block rotates the port is closed. At the same time, as the piston moves toward TDC, air is drawn into the induction chamber though an inlet tract.
The air-fuel mixture is now ignited by a spark plug and the combustion of the air-fuel mixture then forces the piston downwardly, as the same, again actuating the crankshaft, which in turn rotates the crankcase and hence the cylinder block. As the cylinder block rotates, an exhaust port is opened to allow the hot gases to leave the cylinder. The piston is now returned toward the BDC position. During this motion the inlet tract is closed and a transfer tract is opened such that the lower piston portion squeezes the air out of induction chamber and into the transfer tract, the transfer tract delivering compressed air into the power chamber which is now opening. This air is mixed with fuel, ready for the next power stroke of the engine.
To provide an appropriate volume of air to the power chamber, the induction chamber has a larger diameter than the power chamber. Accordingly, the lower flange of the piston is larger than the upper flange. Furthermore, the upper and lower flanges are concentrically arranged on the stem so as to present an I-shaped cross section, and the connecting rods of the opposing cylinders are laterally spaced apart on the crankshaft.
A disadvantage of this configuration is that the overall size of the cylinder block and therefore the engine is required to be widened to accommodate the larger lower flange of the piston.
To allow air, fuel and exhaust gasses to enter and egress the cylinders, as appropriate, each cylinder has at least one aperture which during rotation becomes aligned with ports within the engine housing. The ports include inlet ports and exhaust ports which are configured to align with the aperture at select intervals during cylinder rotation. For example, the transfer port aligns with the cylinder as is moves toward the BDC position, drawing a fuel air mixture into the cylinder power chamber.
As air, fuel and exhaust gasses must pass from the fixed engine block into apertures which are rotating with the cylinder block, it is important to provide a seal to retain the air, fuel and exhaust gasses whilst allowing the cylinder block to freely rotate. Furthermore, the seals need to be configured such that a sealed passage is defined between the apertures of the cylinders and the inlet ports and exhaust ports.
In particular, the sealing ring needs to provide a sufficient sealing such that hot and pressurised exhaust gases are confined within the exhaust port as the exhaust gases pass between the cylinder block and the engine housing. To achieve this, the seal includes an exhaust port plate with locating hollow dowels which may be received into a receiving blind bore of the engine casing. The hollow dowels and blind bore define a recess into which a spring is able to be housed, the spring biasing the exhaust plate away from the engine housing toward the cylinder block.
A disadvantage of this dowel configuration is that the hot exhaust gases may distort the dowel and/or affect the biasing properties of the spring. This may case the seal between the aperture of the cylinder and the exhaust port in the engine housing to become compromised.
To provide a seal between the connecting rods and the crankshaft housing the crankcase, oil seals are located around and in intimate contact with the connecting rods.
A disadvantage of this configuration is that the oil seals are prone to rapid wear due to the high surface speed of the reciprocating connecting rods.
The engine housing has series of casing plates which define and support various sections of the engine. More particularly, there are three main casing plates, which are spaced apart and coupled together by upper and lower bolts which pass through holes in the casing plates. The space between the casing plates and bolts defines a first cavity in which the cylinder block is housed and a second cavity in which an end of the shaft is housed. In this configuration, a central one the three main casing plates divides the first and second cavities. The central casing plate carries one of the main bearings which receives and supports the crankshaft.
A disadvantage of this configuration is that the forces on the casing plates, in particular, the central casing plate are conferred to the bolts. Another disadvantage is that the configuration of the bolts may not hold the casing plates in strict alignment which is important to maintain alignment of the main bearings and the crank shaft.